Connected vehicle communication technology can be applied to active road safety. In a connected vehicle network environment, many applications of the connected vehicle communication technology require vehicle statuses to be broadcasted, such as Intersection Movement Assist (IMA), Left Turn Assist (LTA), Lane change warning (LCW), Forward Collision Warning (FCW) and Electronic Emergency Brake Light (EEBL), via a standard inter-vehicle Basic Safety Message (BSM). Vehicle communication mode includes Vehicle-to-Vehicle (V2V), Vehicle-to-Roadside (V2R) and Vehicle-to-Infrastructure (V2I), or the so-called V2X communication. Wireless Access in Vehicular Environments (WAVE)/Dedicated Short Range Communications (DSRC) is a communication technique applied to the V2X communication.
Advanced Driver Assistance Systems (ADAS) assists in driving a vehicle. However, in an ADAS system, the Non-Line-Of-Sight (NLOS) problem cannot be solved. In a road safety application, crossroad collision and forward vehicle's abrupt stop belong to NLOS accidents.
In recent years, roadside unit safety application has become a popular issue. According to the data from National Highway Traffic Safety Administration (NHTSA), the majority of accidents occurs at a crossroad. NHTSA and Depart of Transportation published an Advance Notice of Proposed Rulemaking (ANPRM) to prompt the Government to legislate that the vehicles running in the United States shall be equipped with the V2V technology. In the near future, compact cars and pickups are required to have the V2V function. The V2V application has to be operated in an environment in which all vehicles are equipped with an On-Board Unit (OBU). However, many vehicles, pedestrians and even other moving objects do not have any OBU equipped. Therefore, accidents are more likely to occur at crossroads, and crossroad safety is severely affected.